This Virology Developmental Research component is designed to utilize and develop virological markers to investigate virus replication at the levels of DNA synthesis (reverse transcription) and gene expression. In addition, these various markers of viral replication would be utilized to investigate viral resistance profiles of individuals infected with human immunodeficiency virus type 1 (HIV-1). The UCLA patient population of the ACTG is ideal for this purpose. 1. To determine if a correlation exists between advanced clinical disease and/or virus expression and expression of viral regulatory genes. 2. To determine the viral resistance profiles of individuals infected with HIV-1 utilizing an in vitro assay on once-passaged isolates or directly on virus from plasma and peripheral blood mononuclear cells (PBMC) (ex vivo). 3. To develop novel assays utilizing PCR to directly monitor the extent of HIV-1 reverse transcription following infection. These assays will be used to monitor the degree of resistance to reverse transcriptase inhibitors of virus from ACTG patients.